Fluidized bed and slurry polymerization systems, particularly staged reactor systems, can suffer from significant variation in the polymer properties of varying particle size fractions. Large variations in polymer properties across particle size can lead to difficulty in mixing the different particles during, for example, pelletization. If all of the granular particles are of similar properties, mixing will occur readily. However, if one or more fractions of particles are of substantially different molecular weight or density, melting during a pelleting operation will not be uniform. Nonuniform pelletization can, in turn, result in:                1. “unmelts”—pellets that still have some areas of relatively undispersed granular which may cause gels or imperfections in finished articles;        2. very high gel count pellets which can occur when granular particles are of significantly different viscosity when melted, i.e. a large molecular weight variation across particles, leading to very high gel counts in thin sheets or films; and        3. an inability to use the resin in granular form as exiting from the final reactor due to substantial differences in molecular weight or density that prevent direct granule users, such as rotational molders, or fabricating extruders, such as blow molders, from utilizing the product due to poor mixing and high gel counts.        
Such variation in polymer properties across particle size fractions occur more significantly when dual or linked reactors are used in the polymerization process, giving an even greater potential for formation of polymer granules with widely divergent properties. For example, if the polymer exiting the first reactor substantially differs in polymer properties across the particle size range, this disparity will continue and be further exacerbated in the second reactor.
To address this situation, the current approach is to employ very small catalyst particles which will produce very small polymer particles. Once used in applications, these very small polymer particles do not appear as a gel even with broad compositional distributions.
A catalyst system useful across a broad range of catalyst particle size and which produces polymers that may be compounded to produce very low gel counts would be very desirable.